Telescope boost at Parkes wins Tristan prize

Prize winner:

Tristan Reynolds, an ASTRO 3D PhD student at the University of Western Australia was awarded the ICRAR/UWA Ken & Julie Michael student prize in February for his work using a modified ASKAP phased array feed (PAF) installed on the Parkes 64m radio telescope.

Updated telescope technology:

To stay scientifically competitive, telescopes must have the latest technology. The continuous improvement of these instruments is what keeps a telescope current.

The Parkes radio telescope is now 10,000 times more sensitive than when it was first built. This is due to improvements beyond the dish itself. Traditionally, a single-dish radio telescope such as Parkes sees only one spot or pixel on the sky at a time. Repeated scanning by the telescope builds up the images.

Phased array feeds (PAFs) are new technology that speeds up scanning. PAFs allow us to electronically synthesise a multi-pixel image of the sky. These feeds can “ignore” radio signals from satellites that would otherwise blind the receivers. It is what the Australian Square Kilometre Array Pathfinder (ASKAP) in Western Australia uses. And these PAFs allow astronomers to increase a telescope’s “field of vision” to build up their knowledge of the sky.

Tristan’s results:

In this work, Tristan investigated the scientific potential of installing a permanent PAF at Parkes. He compared known objects from the older multibeam receiver with newer PAF data.

One of the key results he was able to demonstrate was that PAFs can bypass a major technical limitation which is the so-called ‘standing waves’ that afflict single-dish spectral line observations. These are due to incoming radiation being reflected from the receiver and telescope support structure and self-interfering. He also demonstrated that it is possible to mitigate and suppress radio frequency interference (RFI) from satellites and telecommunications, using a PAF.

After verification, Tristan carried out an experiment using spectrum stacking of neutral hydrogen. Neutral hydrogen (or HI) is a normal, electrically neutral hydrogen atom with one proton and one neutron. It is found throughout galaxies in clouds or external to galaxies as part of the intergalactic gas. It is detected via the 21cm frequency of radio waves. HI clouds were used to determine the structure of our Galaxy from our location within it. Spectral stacking is the process of adding the “spectra” or signatures of individual galaxies. The goal is to recover the average HI signal. This method can be useful for studying very faint signals of galaxies which are below the limits of current radio telescopes.

Tristan made a detection from the stacked spectrum of 1100 galaxies, which were individually undetectable. He also made the most sensitive observation so far of diffuse recombination-line emission from positronium (an atom consisting of an electron and a positron) in the Galactic Centre, placing a tighter upper limit for diffuse emission than any previously published attempt.